Periphyton in Marble Canyon of the Colorado River

Filamentous algae grows in profusion in the Colorado River below Glen Canyon Dam. The photo was taken at Lees Ferry.

The deep release from the dam provides clear water, nutrients, constant temperatures and few floods to scour the bed, so algae grows in profusion and supports an abundant fishery for rainbow trout. The cold waters from the dam, however, are little help to the endangered humpback chub in the river.